Synlett 2008(16): 2471-2474  
DOI: 10.1055/s-2008-1078055
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Direct Asymmetric Aldol Reaction Catalyzed by an Imidazolium-Tagged trans-4-Hydroxy-l-proline under Aqueous Biphasic Conditions

Marco Lombardo*a,b, Filippo Pasia, Srinivasan Easwara, Claudio Trombini*a,b
a Dipartimento di Chimica ‘G. Ciamician’, Università degli Studi di Bologna, via Selmi 2, 40126 Bologna, Italy
b Consorzio Interuniversitario Nazionale ‘La Chimica per l’Ambiente’, via delle Industrie 21/8, 30175 Marghera (VE), Italy
Fax: +39(051)2099456; e-Mail: marco.lombardo@unibo.it; e-Mail: claudio.trombini@unibo.it;
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Received 26 June 2008
Publikationsdatum:
12. September 2008 (online)

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Abstract

Imidazolium-tagged trans-4-hydroxy-l-proline, recently reported by us as an efficient catalyst for the asymmetric cross-aldol reaction in [bmim][Tf2N], gives much better results in terms of catalytic activity and stereochemical performance under aqueous biphasic conditions, providing aldols with anti/syn ratios up to 98:2 and ee (anti) up to 99%. The peculiar solubility properties of imidazolium-tagged trans-4-hydroxy-l-proline ensure an efficient separation of the product from the catalyst and the recycling of trans-4-hydroxy-l-proline for five times without appreciable loss of catalytic activity and stereochemical performance.